#include<stdio.h>
long int factorial(int n)
{
    if(n==0)
    {
        return 1;
    }
    else
    {
        return n*factorial(n-1);
    }
}
int main()
{
    int num;
    scanf("%d",&num);
    if(num<0)
    {
        printf("Inva;lid input");
        return 0;
    }
    long int result = factorial(num);
    printf("%1d",result);
    return 0;
}